The subject invention is directed toward a container having an improved hinge, and more particularly toward a clamshell container formed from a flexible material having a hinge which operates smoothly and without buckling.
Clamshell containers are widely used in the fast food industry. These containers are often formed from a flexible material such as paperboard, and are sturdy enough to protect food products being carried off the restaurant premises for consumption elsewhere. They are also adequately inexpensive that they can be used as serving containers for eat-in customers. Such containers are generally manufactured and shipped in an open configuration, filled with a food product by a restaurant employee, and then closed and given to a consumer. The consumer opens the container to gain access to the product can close the container if necessary to save the food for later.
Clamshell containers comprise a tray portion and a lid portion connected to the tray portion by a hinge on the rear wall of the container. In known containers, the hinge is typically a fold line which allows the paperboard material of the container to fold when the lid is opened. However, this arrangement often causes the rear wall of the container to buckle when the container is opened or closed. This occurs because the rear wall of the container is often slightly bowed, especially when a food product is placed in the container. Therefore, the fold line is not linear, and this non-linear fold line does not fold easily. The rear wall of the container must be deformed considerably when opening a typical container, and this makes the container awkward to use.
Numerous attempts have been made to address this problem. For example, U.S. Pat. No. 5,388,758 to Scovell and U.S. Pat. No. 4,792,085 to Waring use a plurality of cut lines around the center of the hinge or fold line to allow the back wall to buckle more readily. These arrangements reduce the problems caused by the buckling of the back wall, but do not address the problem directly.
U.S. Pat. No. 5,332,147 to Sorenson addresses the problem by providing a slit along the fold line of the hinge and by providing at least one additional slit spaced above or below the hinge fold line. These slit allow a localized bending that relieves stress on the rear wall and reduces rear wall buckling. While Sorenson shows the promise of using a stress relief approach to reducing buckling, the structure taught by this reference does not completely eliminate the problem of buckling.
It would therefore be desirable to provide an improved clamshell container having a hinge that absorbs stresses imparted to the container rear wall when the lid is moved between open and closed positions and that substantially prevents the buckling of the container rear wall.
This problem is addressed by the present invention by providing a clamshell container with an improved hinge that does not lie along a single fold line. Instead, the hinge of the present invention includes a first partial hinge portion extending inwardly from a first side of the container and a second partial hinge portion extending inwardly from the second side of the container, which portions are not collinear.
In a preferred embodiment, the first hinge portion comprises a first fold line or line of weakness extending inwardly from a first edge of the container for a short distance and a first slit that extends inwardly from the end of the first fold line to a point spaced apart from the second side wall of the container. The wall portion between the second end of the first slit and the second wall is not scored or otherwise weakened and thus will resist bending when the container is opened. The second hinge portion is substantially identical to the first hinge portion, but extends inwardly from the second side of the container so that the slits are disposed in a parallel and spaced-apart relationship.
This arrangement provides a flexible strip defined by the first and second spaced apart slits, which strip twists where the container is opened or closed. The stresses that would normally be distributed across the rear wall of the container are instead localized along this strip. Twisting the narrow strip requires little effort, and thus the strip twists and relieves stress while deforming in a manner that is hardly noticeable to a user. Significantly, the presence of a single fold line at opposite ends of the two strips creates offset regions where folding can take place. These offset regions and the offset fold lines allow the lid of the container to pivot slightly during opening and absorb some of the force that otherwise would have buckled the rear wall of a container without this hinge arrangement.
A blank for forming a container according to the invention is also disclosed.
It is therefore a principal object of the present invention to provide a container having a stress-relieving hinge.
It is another object of the present invention to provide a clamshell container with a rear wall that does not buckle when the container is opened and closed.
It is a further object of the present invention to provide a container hinge having first and second offset partial hinge portions.
It is still another object of the present invention to provide an arrangement of fold lines and slits in the rear wall of a clamshell container to minimize buckling when the container is opened and closed.
It is still a further object of the present invention to provide a blank for forming an anti-buckle clamshell container.